Vapors of water and other liquids are used in many applications in current advanced technology processes, including processes employed in micro-electronics manufacturing, as well as in clean room and medical applications. Desirably, such vapors should introduce minimal impurities into a process, such that they can be used, e.g. for the oxidation of silicon, in the production of thin gate oxides (e.g. in the electronics and micro-electronics industries), and in ultra-high purity cleaning processes. However, delivery of liquid vapor (such as, e.g., water, alcohols, or amines) to a process using conventional methods is difficult, and the choices limited to direct liquid injection (DLI) or bubblers, each of which tend to introduce contaminants along with liquid vapor.
In the medical industries, water vapor can be used for humidification. Such water vapor when produced using conventional systems can yield a product having, e.g. prions, viruses, allergens, proteins, bacteria, and other biologically active macromolecules or substances present. Additionally, inorganic substances, such as borates and silicates or metallic substances such as iron, nickel, chromium, copper, and other toxic metals can be present.
Typically, water for micro-electronics applications is produced by reacting gaseous hydrogen and oxygen to yield water vapor. The production of pure water vapor is practically impossible due to the presence of residual oxygen and/or hydrogen remaining in the product water vapor. Removing these components often requires additional expensive and complex separation processes. Additionally, high concentrations of gaseous hydrogen are often required for the synthesis reaction with oxygen, which is conducted at high temperatures well above the explosive limit of hydrogen (approximately 8% at a pressure of approximately 100 kPa).
The simple boiling of high purity de-ionized water to yield water vapor can avoid the problems and dangers inherent in the direct reaction of hydrogen and oxygen to yield steam. However, removing dissolved gases can be difficult and often requires multiple boiling/condensation cycles in a hermetically sealed environment, which can be expensive. Moreover, aerosols containing materials that are not normally volatile, such as salts or metals, can be produced during the boiling process and can add unwanted impurities.